Tesla's valuation makes a lot of very positive assumptions about its potential, but the stock's recent performance does not yet summon the ghosts of the dotcom bubble, says one analyst.

Speaking on Wednesday's edition of "Power Lunch," Bernstein analyst Toni Sacconaghi said bears have good reason to wonder how Tesla's business justifies its current stock price, which has reached all-time highs in recent weeks.

Indeed there is a "very robust set of assumptions that are built into its valuation," Sacconaghi said. "You effectively have to believe that Tesla becomes BMW or Mercedes in size with superior profit margins to justify the valuation. The big debate is: can they do that?"

Investors probably won't know the answer to the question for another year "but that is the key to the story," he said.

"The believers would say 'we are all in on automotive,'" he said, "'and you can't imagine how this company might change the world in other ways going forward.' The bears would say 'we are having trouble making the economics work.'"

On a conference call Wednesday, discussing Greenlight's first-quarter earnings, Einhorn noted that the firm lost money on its short position in Tesla, as the stock reached all-time highs in recent weeks.

He added that the "enthusiasm for Tesla and other bubble basket stocks is reminiscent of the March 2000 dotcom bubble," where investors "rejected conventional valuation methods for a handful of stocks that seemingly can only go up."

Sacconaghi said he would agree with a skeptic's assessment that Tesla's valuation "embeds a very, very positive outlook, either about the automotive market or about a new set of businesses that Tesla can build going forward."

"So I can see both sides," he said, "but I don't agree with the contention that this is something reminiscent of the bubble we saw in the late 90's."

In particular, bears have suggested that Tesla may not be able to scale up its production of the car fast enough to meet demand and edge out competitors, and they have also suggested that Tesla cannot make money selling the car at such a low price. Einhorn is among those skeptics.

And Sacconaghi said he sees Einhorn's point. "I think if you look at the hard economics," Sacconaghi said, "it is tough to believe that the Model 3 will be a really profitable car, given where they are priced at."

On the other hand, Tesla has defied wisdom before. "No one thought they could build an electric car, no one thought a new car company could start in the US and manufacture in the US, and they did it," he said.